Nonlinear resistors of bulk type

ABSTRACT

A NONLINEAR RESISTOR WHEREIN THE NONLINEARITY IS DUE TO THE BULK THEREOF AND WHICH HAS A HIGH N-VALUE COMPRISES A SINTERED BODY OF A COMPOSITION COMPRISING ZNO AND 0.05 TO 10.0 MOLE OF BI2O3. SUCH A NONLINEAR RESISTOR HAS NONOHMIC RESISTANCE DUE TO THE BULK ITSELF, AND THE C-VALUE CAN BE CHANGED WITHOUT IMPAIRING THE NVALUE. OHMIC ELECTRODES ARE APPLIED TO OPPOSITE SURFACES OF THE SINTERED BODY. THE PRESENCE OF OTHER SPECIFIED OXIDES TENDS TO RAISE THE N-VALUE.

y 15, 1972 TAKESHI MASUYAMA L 3,553,453

NONLINEAR RE SISTORS OF BULK TYPE Filed Sept. 27. 1968 TAKESHI MASUYAMA, MICHIO MATSUOKA AND TSUYOSHI NISHI Atto'rneys "United States Patent 01 fice 3,663,458 NONLINEAR RESISTORS OF BULK TYPE Takeshi Masuyama, Michio Matsuoka, and Tsuyoshi Nishi, Osaka, Japan, assignors to Matsushita Electric Industrial Co., Ltd., Osaka, Japan Filed Sept. 27, 1968, Ser. No. 763,285

Claims priority, application Japan, Oct. 17, 1967,

42/67,395; Jan. 22, 1968, 43/4,192, 43/4,198;

Feb. 12, 1968, 43/9,311; May 10, 1968, 43/31,772,

Int. Cl. H01b N06 US. Cl. 252--518 Claims ABSTRACT OF THE DISCLOSURE A nonlinear resistor wherein the nonlinearity is due to the bulk thereof and which has a high n-value comprises a sintered body of a composition comprising ZnO and 0.05 to =l0.0 mole of Bi O Such a nonlinear resistor has nonohmic resistance due to the bulk itself, and the C-value can be changed without impairing the nvalue. Ohmic electrodes are applied to opposite surfaces of the sintered body. The presence of other specified oxides tends to raise the n-value.

The invention relates to nonlinear resistors having nonohmic resistance due to the bulk thereof and more particularly to varistors comprising zinc oxide and bismuth oxide.

Various nonlinear resistors such as silicon carbide varistors, selenium rectifiers and germanium or silicon p-n junction diodes have been widely used for stabilization of voltage or current of electrical circuits. The electrical characteristics of such a nonlinear resistor are expressed by the relation:

V n (a) where V is the voltage across the resistor, I is the current flowing through the resistor, C is a constant corresponding to the voltage at a given current and exponent n is a numerical value greater than 1. The value of n is calculated by the following equation:

where V and V are the voltages at given currents I and I respectively. The desired value of C depends upon the kind of application to which the resistor is to be put. It is ordinarily desirable that the value of n be as large as possible since this exponent determines the extent to which the resistors depart from ohmic characteristics.

Nonlinear resistors comprising sintered bodies of zinc oxide with or without additives and silver paint electrodes applied thereto, have previously been disclosed. The nonlinearity of such varistors is attributed to the interface between the sintered body of zinc oxide with or without additives and the silver paint electrode and is controlled mainly by changing the compositions of said sintered body and silver paint electrode. Therefore, it is not easy to control the C value over a wide range after the sintered body is prepared. Similarly, in varistors comprising germanium or silicon p-n junction diodes, it is difficult to control the C-value over a wide range because the nonlinearity of these varistors is not attributed to the bulk but to the p-n junction. On the other hand, the silicon carbide varistors have nonlinearity due to the contacts among the individual grains of silicon carbide bonded together by a ceramic binding material, i.e. to the bulk, and the C-value is controlled by changing a dimension in the direction in which the current flows through the varistors. The silicon carbide varistors, however, have a relatively low n-value ranging from 3 to 6 and are prepared by firing in non-oxidizing atmosphere, especially for the purpose of obtaining a lower C-value.

An object of the present invention is to provide a nonlinear resistor having nonlinearity due to the bulk thereof and being characterized by a high n-value.

Another object of the present invention is to provide a method for making a nonlinear resistor having the nonlinearity due to the bulk thereof and being characterized by a high n-value, without using non-oxidizing atmosphere.

These and other objects of the invention will become apparent upon consideration of the following description taken together with the accompanying drawing in which the single figure is a partly cross-sectional view through a nonlinear resistor in accordance with the invention.

Before proceeding with a detailed description of the nonlinear resistors contemplated by the invention, their construction will be described with reference to the aforesaid figure of drawing wherein reference character 10 designates, as a Whole, a nonlinear resistor comprising, as its active element, a sintered body having a pair of electrodes 2 and 3 in an ohmic contact applied to opposite surfaces thereof. Said sintered body 1 is prepared in a manner hereinafter set forth and is in any form such as circular, square or rectangular plate form. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3, respectively, by a connection means 4 as solder or the like.

A nonlinear resistor according to the invention comprises a sintered body of a composition comprising zinc oxide and 0.05 to 10.0 mole percent of bismuth oxide, and ohmic electrodes applied to opposite surfaces of said sintered body. Such a nonlinear resistor has non-ohmic resistance due to the bulk itself. Therefore, its C-value can be changed without impairnig the n-value by changing the distance between said opposite surfaces. The shorter distance results in the lower C-value.

The higher n-value can be obtained when said sintered body comprises 99.9 to 99.0 mole percent of zinc oxide and 0.1 to 1.0 mole percent of bismuth oxide in accordance with the invention.

Said ohmic electrodes can be made of an electroless plated or electrolytic plated film of Ag, Cu, Ni or Sn, a vacuum evaporated film of Al, Zn, Sn or In or a metallized film of Cu, Sn, Zn or Al in accordance with the prior well known technique.

According to the present invention, the n-value is elevated when said sintered body consists essentially of 80.0 to 99.9 mole percent of zinc oxide, 0.05 to 10.0 mole percent of bismuth oxide and 0.05 to 10.0 mole percent, in total, of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum oxide, tantalum oxide, iron oxide, and chromium oxide. Superior results are obtained with compositions having 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 1.0 mole percent of bismuth oxide and 0.1 to 5.0 mole percent, in total, of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum oxide, tantalum oxide, iron oxide and chromium oxide.

According to the present invention, the resistor has an extremely high n-value when when the sintered body consists essentially of 85.00 to 99.85 mole percent of zinc oxide, 0.05 to 5.0 mole percent of bismuth oxide, 0.05 to 5.0 mole percent of cobalt oxide or manganese oxide and 0.05 to 10.0 mole percent of, in total, at least one member selected from the group consisting of boron oxide, barium oxide, indium oxide, antimony oxide, titanium oxide and chromium oxide.

The optimum results are obtained with a sintered body consisting essentially of 84.00 to 99.80 mole percent of zinc oxide, 0.05 to 5.00 mole percent of bismuth oxide, 0.05 to 3.00 mole percent of cobalt oxide, 0.05 to 3.00 mole percent of manganese oxide and 0.05 to 5.00 mole percent of, in total, at least one member selected from the group consisting of boron oxide, barium oxide, indium oxide, antimony oxide, titanium oxide and chromium oxide.

The sintered body 1 can be prepared by a per se well known ceramic technique. The starting materials in the compositions described in the foregoing description are mixed in a wet mill so as to produce homogeneous mixtures. The mixtures are dried and pressed in a mold into desired shapes at a pressure from 100 kg./cm. to 1000 kg./cm. The pressed bodies are sintered in air at a given temperature for 1 to 3 hours, and then furnace-cooled to room temperature (about to about 30 C.).

The sintering temperature is determined from the view of electrical resistivity, nonlinearity and stability. The zinc oxide sintered body having a single addition of bismuth oxide is advantageously fired at a temperature of 800 to 1200 C. The body sintered at a temperature higher than 1200 C. shows low electrical resistivity and poor nonlinearity. With respect to the aforesaid sintered body of zinc oxide having a combined addition of bismuth oxide and at least one metal oxide selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum oxide, tantalum oxide, iron oxide and chromium oxide, the advantageous firing temperature ranges from 1000 to 1450 C.

The pressed bodies are preferably sintered in non-oxidizing atmosphere such as nitrogen and argon when it is desired to reduce the electrical resistivity. The electrical resistivity also can be reduced by air-quenching from the sintered temperature to room temperature even when the pressed bodies are fired in air.

The mixtures can be preliminarily calcined at 700 to 1000 C. and pulverized for easy fabrication in the subsequent pressing step. The mixture to be pressed can be admixed with a suitable binder such as water, polyvinyl alcohol, etc.

It is advantageous that the sintered body be lapped at the opposite surfaces by abrasive powder such as silicon carbide in a particle size of 300 meshes to 1500 meshes.

The sintered bodies are provided, at the opposite surfaces thereof, with aforesaid ohmic electrodes in any available and suitable method.

Lead wires can be attached to the silver electrodes in a per se conventional manner by using conventional solder having a low melting point. It is convenient to employ a conductive adhesive comprising silver powder and resin in an organic solvent in order to connect the lead wires to the silver electrodes.

Non-linear resistors according to this invention have a high stability to temperature and in the load life test, which is carried out at 70 C. at a rating power for 500 hours. The n-value and C-value do not change remarkably after heating cycles and load life test. It is advantageous for achievement of a high stability to humidity that the resultant nonlinear resistors are embedded in a humidity proof resin such as epoxy resin and phenol resin in a per se well known manner.

A more preferable method for making a non-linear resistor contemplated by the invention Comprises providing a sintered body of zinc oxide with or without 0.1 to 5.0 mole percent in total, of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum oxide, tantalum oxide, iron oxide and chromium oxide: coating the opposite surfaces of said sintered body with a paste including, as a solid ingredient, bismuth oxide powder; firing the coated body at a temperature of 600 to 1200 C. in oxidizing atmosphere so as to diffuse bismuth ions into the bulk of said sintered body; cooling the bismuth diffused sintered body to room temperature; and applying aforesaid ohmic electrodes to opposite surfaces of the resultant body. Said sintered body can be prepared in a per se well known ceramic technique, i.e. by heating a pressed body in a given composition at a temperature of 1000 to 1450 C. for 1 hour in air or non-oxidizing atmosphere such as nitrogen gas or argon gas.

Said paste comprises, as a solid ingredient, bismuth oxide powder and an organic resin such as epoxy, vinyl or phenol resin in an organic solvent such as butyl acetate, toluene or the like. Said bismuth oxide can be replaced with any bismuth compound such as bismuth carbonate or bismuth hydroxide which is converted into bismuth oxide when heated at 600 to 1200 C. Operable weight proportion of said bismuth oxide to organic solution is 20 to wt. percent of bismuth oxide and the remainder of organic solution. According to the present invention, the n-value is extremely elevated when bismuth oxide as a solid ingredient in the paste is incorporated with cobalt oxide and/or manganese oxide. Operable and advantageous weight proportions of said solid ingredients are shown in Table 1.

TABLE 1 Weight part;

Bismuth Cobalt Manganese oxide oxide oxide Operable proportion 28 2-8 2-8 2-8 Superior proportion 2-8 1-2 1-2 TABLE 2 Bi O; B 0 SiOz C00 MnO 50-84 8-25 8-25 Operable weight percent 48-80 8-23 8-23 4-16 48-80 8-23 8-23 4-10 Superior weight percent 40-70 10-20 10-20 5-10 5-10 Said glass frit in a powder form is dispersed in an organic solvent such as butyl acetate, toluene or the like dissolving organic resin such as epoxy, vinyl and phenol resin. Care should be taken that said glass frit does not include alkali metal ions in a monovalence such as lithium ions, potassium ions or sodium ions. Operable weight percent desirable paste is 20 to 60 weight percent of glass frit in a powder form, 20 to 40 weight percent of said organic resin and 20 to 40 weight percent of said organic solvent.

The diffusion temperature and time depend on the weight percent of bismuth oxide in said paste and should be controlled so that the diffused bismuth oxide distributes uniformly throughout the sintered body of zinc oxide and is in an amount of 0.1 to 1.0 mole percent. The higher diffusion temperature requires the shorter diffusion time.

Such a diffusion technique produces a sintered body having a n-value higher than that of a sintered body prepared by sintering a mixture of 99.9 to 99.0 mole percent TABLE 4 Electric characteristics of resultant resistors Starting materials (mole percent) (at 2. Further additives given current B120 Type Amt. of 1 ma.)

ZnO

of zinc oxide and 0.1 to 1.0 mole percent of bismuth oxide or a 99.8 to 94.0 mole percent of zinc oxide, 0.1 to 1.0 mole percent of bismuth oxide, and 0.1 to 5.0 mole percent of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, 5 antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum ,r.t.tf d..n m n u wmm rm a o m mm w .21 mama nmmma manwwmmaamane snc a xdm mm m m mn y 2 3 mm eeweamammmnmmnamamnmam a namaweawnnmanmmmameseesa e e c a o m m ohdm ne a mm 1 1 31 21 31 a a 1 2 2 1 1 12803n95 Mm T O o .W l mmnnr mm c m m E 6 t m d wm m m m m 0 Huh t m mjjjr rjrjrjjjjjnsj 555505505555m o%250555555 n O f g ..H C m g m 000000000000000100 .00005 0 0 L00 00..02 a00 0 0 00 ieh n ri v..1 w A 0 00 1 T hsneem wS h ev I 3 eT mt t knavt mu wh .r X .1 n mm E m awom,mx s mk s m d e I 0 6 0 mm H me me mue a w a w I w mwnm a mwm M a m fm n m m w T m BmsTcBBmsTc s A mn wmk x mwoom .uh A 8 2 5 55555555555 0 c m fi m w n T m o 00000000000 a Hind m m C it. dn efl d s m 1m p6 n W 0 555505555555 m m m m T055555 .ae t sg ,toea r o 000 .1 0000000 0000 00 0 n dmmmmm o m m c 0 III mnmmu bmm m wm m III m I m a O X a g 3 555555555555555555555555 c e o m .m 0 00000000000000000000000 :1 n d x. o a I ma reomomunmt a I M mmMn m m hs m t6 w se .wn b r gU O 0N... fS aflwou wh u n .0 WWW fiabctlciclipc Z 5 0 5 0 5 O 5 0 5 0 m 1 2 2 3 3 4 4 5 5 6 6 a C3 60836 S eV.6 h m n 321334500803 t ns w n a n 134 1444434443 w1m m% Wv 6 .l a t 36 W a mm rw wc fi f a al. rcd f et tw dn aiSk e .l 0 d S Ol/Tb 3 Ed 0 r. 8 we 4345310036 5.1 .m I S M m a n.E%S mmm m W 4 80423455fi v Ad C6 8 n neuH ncbi r bd t k 0 L t r ha 1 me no. eP H l 6 0 3 a On any w m d.w mmcdmefle bmm m.. .mu e..w f w w m m e 9 na amm awwvm m am w e m n 1 r r. q t. ,T.. C (e S S.l .1 .1 .SC V. CB 9 mm a mm mmm mwm m mmmm m m mmmwmmm hb 3 08 r. S c 6 6 a C a3.n 2 t t.. C um e .mm m mmw mem m 00 .0 5 .00 mm mm mmw n 1 u m mo a w m bm m 1111L2.L0011111 2 M d M a8 a 8 n c T C e t. k 0 0 n V E T S5 l .ly C. Rh 0 3 w E 0% rf.lennl 6. S &10 :106 T3 d h t hR 3 d L 62 dao SWHIU. T nU E L t S a P n r e ,5 fe k e c L T P 2r .r f m M l d fl311 mw md md l ymoo B 2.9) 00000000000000 M me m d m c a ma m u mmm A mac awwmawmmmmmwmw A mm m m 1 a S mm... m mr .atwma w ao m T ea. rttiirt X awnaemam .1 S E OOem Nde ne m C em d w 11 flm mm SCNMS m w 1 mm mC n W.% flm afu WXe e Sm YM h0 nC.E m d armaJdlePcncmrpemmenome t a dnCt61rmH Dowe nwsvm hu ah flca 3 22222222251500 .HS w fm m 6 i kbmu 58C .10.. .5 C b 0 U6 mmm m n .mm.we .m.mo mfi m0 m 00000000000015 Mm d m m m m u m5m e .n d a m 0 am t z e 11 3S r v e m .1 m m S UT.10..HV. w mnmammmmwmmmmm m mm m m m m m m mam mu me aedwmm a aw m m m a aw JSUU n-le m 6 m w m .llm eee o m 0a am 3 e rePi .tr u t a t e dme atm n wma n mmamem mm 5:; m mnm. maaeh n v e m wn m s m 3 3303339000 mm o mn o .m w on. mrammmoadmummb z mam aawaaaaaa Pa h1oaa w EXAMPLE 4 A sintered body of pure zinc oxide is prepared by pressing zinc oxide powder at 340 kg./cm. and heating the pressed body for 1 hour at a temperature listed in Table 6. After being cooled to room temperature, the oxide, barium oxide, nickel oxide and chromium oxide; 70 sintered body is lapped at both opposite surfaces with silicon carbide abrasive. The lapped surfaces are coated with a paste containing wt. percent of bismuth oxide in an epoxy resin butyl alcohol solution. The applied paste is fired at the temperature listed in Table 6 for 30 75 minutes in air. A chemical analysis of the fired body indiknown technique. Lead wires are attached to the aluminum electrodes by means of conductive silver paint. The electric characteristics of the resultant resistor are shown in Table 4. -It will be readily understood that the n-value can be remarkably elevated by a further addition of one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, tin

the C-value at a given current of 1 ma. can be lowered remarkably by a further addition of one member selected from the group consisting of titanium oxide, boron oxide, aluminum oxide, molybdenum oxide, tantalum oxide and iron oxide.

cates that bismuth oxide diffuses into the sintered body of zinc oxide. Then A] electrodes and lead wires are attached to the opposite surfaces of the sintered disc in the same manner as that described in Example 1. The electric characteristics of the resultant resistor are shown in Table 6. It will be readily understood from comparison between Tables 3 and 6 that the n-value of the resistor can be elevated greatly by firing-on paste containing bismuth oxide.

A mixture of a composition listed in Table 7 is pressed, fired in the same manner as that described in Example 2. The sintered body is lapped at opposite surfaces and is covered at the opposite surfaces 'with paste according to Example 4. The paste applied to the opposite surfaces is fired at 800 C. for 30 minutes in air. Then Al electrodes and lead wires are attached to the opposite surfaces in the same manner as that set forth in Example 1. The electric characteristics of the resultant resistor are shown in Table 7. It will be readily understood from a comparison between Tables 4 and 7 that the n-value of the resistor can be elevated greatly by using paste containing bismuth oxide.

TABLE 7 Electric characteristics of Starting materials (mole percent) resultant resistors Amt. 1 ma.)

EXAMPLE 6 -A mixture of a composition listed in Table 8 is pressed in the same manner as that set forth in Example 1. The pressed body is sintered in air at the temperature listed in Table 8 for 1 hour and then furnace-cooled to room temperature. The sintered disc is completed to the nonohmic resistor in the same manner as that described in Example 5. The electric characteristics of the resultant resistor are shown in Table 8. It will be readily understood that the n-value of the resistor can be elevated greatly by using paste containing bismuth oxide as seen from a comparison between Table and 8.

TABLE 8 Electric characteristics of resultant Starting materials (mole percent) resistors Further Sintering C (at a additives tempergiven atures current ZnO CoO M1102 Type Amt. C.) of 1 me.) n

EXAMPLE 7 A mixture of a composition of Table 9 is pressed and fired in the same manner as that set forth in Example 2. The sintered body is lapped at the opposite surfaces and covered at the opposite surfaces with a paste containing solid ingredients as listed in Table 9. The paste applied to the opposite surfaces is fired in air at 800 C. for 30 minutes. Then Al electrodes and lead wires are attached to the opposite surfaces in the same manner as that described in Example 1. The electric characteristics of the resultant resistor are shown in Table 9.

TABLE 9 Electric Weight percent of characteristics Starting materials solid ingredients of resultant (mole percent) (percent) resistors Additives 2110 Type Amt. B; 11

99.5 M1102 0.5 70 40 19.5 99.5 B 03 0. 5 70 70 34. 2 99.5 BaO 0.5 70 72 43.4 99.5 ImOs 0.5 70 215 27.3 99.5 81120: 0.5 70 42.1 99.5 T102 0.5 70 24 16.8 99.5 0x20. 0.5 70 158 32.1 99.5 C00 9.5 70 70 24.3 99.5 B20: 0. 5 70 64 37. 5 99.5 B30 0. 5 70 77 43.1 99.5 R1203 0.5 70 220 24.3 99.5 SbzOa 0. 5 70 40. 8 99.5 T102 0.5 90 37 16.6 99.5 C120: 0. 5 70 167 34. 2 100- 70 200 12.7 100.--. 70 180 11. 3 100- 50 25 13.4. 99.5. 50 25 58 38.1 99.5- 50 25 67 43.3 99.5. 50 25 200 32.2 99.5. 50 25 110 45. 8 99.5. 50 25 22 17.2 99.5 50 25 148 35.6

EXAMPLE 8 The resistors of Examples 2, 3, 5, 6 and 7 are tested in accordance with a method widely used in the electronic components parts. The load life test is carried out at 70 C. ambient temperature at 1 watt rating power for 500 hours. The heating cycle test is carried out by repeating 5 times the cycle in which said resistors are kept at 85 C. ambient temperature for 30 minutes, cooled rapidly to -20 C. and then kept at such temperature for 30 minutes.

Table 10 shows the average change rates of C-value and n-value of resistors after heating cycles and load life test.

A mixture of a composition of Table 12 is pressed in the same manner as that set forth in Example 2. The pressed body is sintered in air at 1350 C. for 1 hour and then furnace-cooled to room temperature. The sintered disc is lapped at the opposite surfaces and coated at the opposite surfaces with a paste having a composition set forth hereinbelow. The paste applied to opposite surfaces is fired at 800 C. for 30 minutes in air. The pastes have a solid ingredients composition shown in Table 11 and are prepared by mixing 10 weight parts, in total, of said solid ingredients with 100 weight parts of epoxy resin in 20 to 40 weight parts of butyl alcohol. Then Al electrodes and lead wires are attached to the opposite surfaces in the same manner as that set forth in Example 1. The electric characteristics of the resultant resistor and the change rates after life test carried out in a way similar to that described in Example 8 are shown in Table 12.

TABLE 11 Weight percent B20 SiOz C M110 TABLE 12 Electric charac- Change rates Starting materials teristlcs of after ife test (mole percent) C resultant resistors (percent) ing 0 (ate. Additives mategiven rials current ZnO Type Amt. N o. 1 me.) 'n. 0 1|,

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A nonlinear bulk-type resistor consisting essentially of a sintered body of 80.0 to 99.9 mole percent of zinc oxide, 0.05 to 10.0 mole percent Bi O and 0.05 to 10.0 mole percent in total, of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide, nickel oxide, molybdenum oxide, tantalium oxide, iron oxide and chromium oxide, and ohmic electrodes applied to opposite surfaces of said sintered body.

2. A nonlinear resistor defined by claim 1, wherein said sintered body is of a composition consisting essentially of 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 1.0 mole percent of bismuth oxide and 0.1 to 5.0 mole percent, in total, of at least one member selected from the group consisting of cobalt oxide, manganese oxide, indium oxide, antimony oxide, titanium oxide, boron oxide, aluminum oxide, tin oxide, barium oxide and nickel oxide, molybdenum oxide, tantalum oxide, iron oxide and chromium oxide.

} 3. A nonlinear resistor defined by claim 1, wherein said sintered body is of a composition consisting essentially of 85.0 to 99.85 mole percent of zinc oxide, 0.05 to 5.0 mole percent of bismuth oxide, 0.05 to 5.0 mole percent of cobalt oxide and 0.05 to 10.0 mole percent, in total, of at least one member selected from the group consisting of manganese oxide, boron oxide, barium oxide, indium oxide, antimony oxide, titanium oxide and chromium oxide.

4. A nonlinear resistor defined by claim 1, wherein said sintered body is of a composition consisting essentially of 85.0 to 99.85 mole percent of zinc oxide, 0.05 to 5.0 mole percent of bismuth oxide, 0.05 to 5.0 mole percent of manganese oxide and 0.05 to 5.0 mole percent, in total, of at least one member selected from the group consisting of cobalt oxide, boron oxide, barium oxide, indium oxide, antimony oxide, titanium oxide and chromium oxide.

5. A nonlinear resistor defined by claim 1, wherein said sintered body is of a composition consisting essentially of 84.00 to 99.80 mole percent of zinc oxide, 0.05 to 5.00 mole percent of bismuth oxide, 0.05 to 3.00 mole percent of cobalt oxide, 0.05 to 3.00 mole percent of manganese oxide and 0.05 to 5.00 mole percent of, in total, at least one member selected from the group consisting of boron oxide, barium oxide, indium oxide, antimony oxide, titantium oxide and chromium oxide.

OTHER REFERENCES Chem Abstracts, vol. 59, 104d.

DOUGLAS J. DRUMMOND, Primary Examiner US. Cl. X.R. 

